Samplers are used to take periodic samples from liquids flowing through a process line, e.g. a pipeline. Such liquids include water, crude oil, refined products including: gasoline, diesel, jet fuel, kerosene, etc., natural gas liquids including: liquid ethane, liquid propane, liquid butane, liquid iso-butane, etc. These samplers typically move a shaft up and down to take a sample which is then accumulated with prior samples in a sample collection container or vessel. This movement is sometimes referred to as a “stroke” in the industry. Further, some samplers are inserted and withdrawn from a process line through an isolation valve while the process line remains under pressure and in operation. In some of these samplers, the sample collection head assembly could be adjusted to vary the volume of sample, but this required removal of the sampler from the process line, removal from process pressure and manual disassembly of the sample head assembly which was time consuming, expensive and disruptive to the sample collection process. There is a need to be able to adjust the volume of a sample while the sampler is under process line pressure and while the process line is in operation.
Some liquid pipelines sequentially transport product from different customers and/or from different storage tanks. In one example, switching from different sources of product may occur as frequently as every 105 seconds to intervals as long as three days. Obviously, the switching interval varies and can vary widely beyond the intervals mentioned above.
Some sampling operations take seven liters of sample from each aliquot of product flowing through the line. If the switching interval is long, the volume of sample taken during each stroke of the sampler will be comparatively small. If the switching interval is short, the volume of sample taken during each stroke of the sampler with be comparatively large, in order to accumulate seven liters of sample. There is a need to be able to quickly and easily adjust the volume of sample taken during each stroke of the sampler, without delay or down time and without having to manually disassemble the sample head assembly.